1. Field of the Invention
The present invention generally relates to automatic Gas Tungsten Arc Welding (AGTAW or GTAW) and, more particularly, to narrow groove welding torches for such welding, and to gas diffusers thereof.
2. Related Art
The AGTAW process uses welding equipment which, for a given set of welding parameters (current, voltage, travel speed and the like) performs the weld with minimal adjustments or corrections by the welding operator. As discussed below, particular problems are presented in providing a weld joint in a narrow groove in thick plates or heavy wall pipes.
Typically, a weld prep is determined by a joint geometry which requires the least amount of welding and therefore, reduces distortion and material stresses. However, it is also necessary that the joint geometry provide good accessibility for the welding torch. Welding thick plates or heavy wall pipes requires a weld joint design which allows the welding torch, or at least the electrode thereof, to be placed in the joint and the work angle of the torch adjusted into the side wall to assure a good weld tie-in as a series of weld beads are deposited layer by layer until the joint is filled.
One technique for welding thick plates requires the adjacent surfaces to be machined or otherwise prepared in advance in order to provide a "V" notch having a large volume to accommodate the welding torch. Unfortunately, while more maneuvering room is provided, multiple (24-150) weld beads per layer are required to fill the large volume created for the welding torch. Therefore, the welding process requires additional setup and machining time, preparation, filler material and shielding gas. In addition, the multiple bead layers are subject to distortion and internal stresses that result in decreased weld quality.
In an effort to reduce welding time and cost, a joint design which requires a minimal amount of welding is preferable. Narrow groove welding is a process wherein successive single bead weld layers are applied directly on top of one another in a narrow groove or joint, thus requiring a minimal amount of root opening on the order of 0.250 inches and a 0.degree. side wall.
Briefly considering the difficulties created by the geometry and restrictiveness of the narrow grooves of the type just described, the welding torch or associated hardware must be modified to weld the entire joint from the surface since such a joint design provides insufficient room to angle or maneuver the torch in the joint. In addition, it is difficult to obtain the amount of shield gas in the weld joint necessary to protect the molten weld pool and electrode from atmospheric contamination. Moreover, in an approach where a long bare electrode is inserted into the groove and an associated diffuser is placed outside of the weld joint, there can be problems with the amount of Argon shield gas used to protect the weld pool and electrode. For example, in a confined area or work space, the shield gas rapidly replaces the oxygen available to the welding operator, thereby creating a safety concern. More generally, the high volume of shield gas required also adds to the cost of the weld.